nternational trade is a controversial issue at the Democratic Party convention in Philadelphia.
Senator Bernie Sanders, who unsuccessfully sought the party's Presidential nomination and has given Hillary Clinton his backing, used the event as a platform to express his opposition to one of President Obama's big trade deals.
It's called the Trans-Pacific Partnership or TPP. It has been agreed but not yet ratified. Mr Sanders told the convention, to cheers from his own supporters, that it must not be ratified.
The issue has become even more politically contentious than it already was with groups in both main parties concerned about trade liberalisation agreements.
President Obama has treated them as a priority, while opponents see them as harming the US economy, as driven by big business and as being conducted in excessive secrecy.
The TPP is not the only one, but it is a very big one and the negotiations are complete.